Pdf on amplitude modulation class 12

1. PRINCIPLES OF COMMUNICATION
1. BASICS OF COMMUNICATION
2. AMPLITUDE MODULATION
Created by C. Mani, Principal, K V No.1, AFS, Jalahalli West, Bangalore

2. BASICS OF COMMUNICATION
1. Communication: Processing, sending and receiving of information
2. Information: Intelligence, signal, data or any measurable physical quantity
3. Basic Communication System:
Source of
information
Transmitter
Link
Receiver
Destination
i) Speech
ii) Pictures
iii) Words
iv) Codes
v) Symbols
vi) Commands
vii) Data
i) Oscillators ii) Amplifiers
iii) Filters iv) Antenna
i) Wire Links
ii) Wireless
iii) Optic Fibres
i) Radio ii) TV iii) Computer iv) Telephone
v) Teleprinter vi) Telegraph vii) Fax viii) Internet

3. Forms of Communication: Types of communication:
1. Radio Broadcast
2. Television Broadcast
3. Telephony
4. Telegraphy
5. Radar
6. Sonar
7. Fax (Facsimile Telegraphy)
8. E-mail
9. Teleprinting
10. Telemetering
11. Mobile Phones
12. Internet
1. Cable
communication
2. Ground wave
communication
3. Sky wave
communication
4. Satellite
communication
5. Optic fibre
communication

4. Analogue signal
A continuous signal value which
at any instant lies within the
range of a maximum and a
minimum value.
A discontinuous signal value
which appears in steps in pre-
determined levels rather than
having the continuous change.
Digital signal
0 t
V
1 0 1 0 1 0 1 0 1
T/4 T/2 3T/4 T 5T/4 3T/2 7T/4 2T
t
0
π 2π 3π 4π
π/2 3π/2 5π/2 7π/2 θ = ωt
E
,I E0
I0
E = E0 sin ωt
I = I0 sin ωt

5. MODULATION:
Types of Modulation:
1. Amplitude Modulation
2. Frequency Modulation
3. Pulse Modulation
4. Phase Modulation
Modulation is the process of variation of some characteristic
of a high frequency wave (carrier wave) in accordance with the
instantaneous value of a modulating signal.
Modulator
A.F.
Signal Amp.
Modulated
Signal
H.F. Signal
Oscillator

6. AMPLITUDE MODULATION (AM):
e m= Em sin mt
ec = Ec sin ct
e = (Ec + Em sin mt) sin ct
Modulation Index (ma)= kaEm/Ec
If ka=1, then ma= Em/Ec
e = Ec sin ct + (maEc/2) cos (c - m)t - (maEc/2) cos (c + m)t
(Courtesy: Internet)

7. 1. The Amplitude Modulated wave is the summation of three
sinusoidal waves with the frequencies c, c-m and c+m
namely Original frequency, Lower Side Band frequency and
Upper Side Band frequency respectively.
2. The Bandwidth required for AM, BW = 2 m
3. The amplitude Ec of the unmodulated carrier wave is made
proportional to the instantaneous voltage (e m= Em sin mt)
of the modulating wave.
Voltage
Amplitude
c-m Frequency
Inferences from equation for e:
c c+m
(Courtesy: Internet)

8. Significance of Modulation Index:
maEc= kaEm
Emin
Emax
e
0
Emax = Ec + maEc
Emin = Ec - maEc
Emax - Emin
Emax + Emin
ma =
Generally,
0 < ma < 1
AF signal
ma = 0 (No modulation)
ma = 0.5 or 50%
On manipulating, we get
ma = 1 or 100%
ma > 1 or 100%
Ec

9. Power Relation in the AM wave:
If the modulated wave is applied to a resistor of resistance R
(say antenna circuit), then the r.m.s. power dissipated in the
form of heat is,
Pr.m.s = (1/R)Ec /222 + maEc /222 + maEc /222
Prms = (Ec
2 /2R) 1 + (ma
2 /2) = Pc1 + (ma
2 /2)
(where Pc is power dissipated by unmodulated carrier
wave)
If ma = 1, then Prms  Pmax and Pmax = 3 Pc /2
Similarly, Power carried by both side bands PSB = Prms / 3
which is wasted.

10. 1. AM is an easier method of transmitting and receiving speech
signals.
2. It requires simple and inexpensive receivers.
3. It is a fairly efficient system of modulation.
Drawbacks:
1. AM is more likely to suffer from noise.
2. Appreciable energy is contained by three components of AM
wave. Sufficient energy can be saved by suppressing carrier
wave and one of the side bands. This process makes the
equipment complex.
3. Cost of such transmitters and receivers becomes practically
more.
Advantages:
END